Molded plastic parts are widely used in automobiles, trucks, household appliances, graphic arts, and the like. Frequently these plastic parts are made from polyolefins such as polyethylene, ethylene copolymers, polypropylene, propylene copolymers, and polyolefin blends with other polymers. One such blend is a thermoplastic polyolefin (TPO), which is a rubber-modified polypropylene. Frequently, these plastic parts must be painted to match the color of painted metal parts that are also present in the automobile, appliance, or other item. Typical paints do not adhere well to these plastic parts. Thus, adhesion-promoting primers are needed to improve the adhesion of the paints to the polyolefin materials.
Although chlorinated polyolefins, particularly chlorinated, maleated crystalline polypropylene polymers, are effective for this purpose, they have very limited solubility in anything other than aromatic or chlorinated solvents. The U. S. Federal Clean Air Act of 1990 limits the amounts of solvents on the Hazardous Air Pollutants (HAPs) list that can be used in some areas, and most practical aromatic and chlorinated solvents for use in coatings applications are on the HAPs list. There are some applications where a non-chlorinated adhesion promoter is desired. Other systems proposed for use as primers are based on maleated amorphous polyolefins, which are dissolved in aromatic solvents such as xylene and toluene.
Attempts have been made to provide water-based paints and primers for the automotive and appliance industries, but these systems generally are not thought to be as effective as solvent-based systems. There have been several patents issued pertaining to the modification of polyolefins to provide an adhesion-promoting primer composition for paint topcoats onto polyolefin surfaces.
U.S. Pat. No. 4,146,590 describes reacting crystalline polyolefins in the molten state with an alicyclic carboxylic acid having a cis form non-conjugated double bond in the ring, such as cis-4-cyclohexene-1,2-dicarboxylic acid or endobicyclo [2,2,1]-5-heptene-2,3-dicarboxylic acid, or the anhydride of either; or an unsaturated carboxylic acid or anhydride, such as maleic anhydride or acrylic acid, resulting in a modified crystalline polyolefin having residual carboxylic acid monomer present. The polyolefin is thereafter reacted with a polyhydric alcohol or a polyamine, to thereby fix the residual monomer into the polymer. The crystalline nature of these modified polyolefins makes them practically insoluble in solvents used for liquid coatings, and therefore unsuitable for liquid coating compositions. These polymers are instead used as coatings in the solid state, requiring further heating, melting, and molding of the polymer. The fixing of the residual monomer to the polymer is taught to decrease the odor that would otherwise result from release of the monomer during the subsequent heating, melting, and molding of the polymer.
U.S. Pat. No. 4,299,754 describes a method for producing a modified propylene-ethylene copolymer, by graft copolymerization with maleic acid or anhydride. The propylene ethylene copolymer has a propylene content of 50 to 75 mole percent and a crystallinity, determined by an X-ray diffraction method, of 2 to 20%. The amount of maleic acid or maleic anhydride grafted is 0.5 to 15% by weight. The modified polymer has an intrinsic viscosity of at least 0.3, and is dissolved in the organic solvent in a concentration of 10 to 100 kg/m3 of solvent. The resulting treating agent is suitable as an undercoat of the polyolefin articles and permits coating of a paint with markedly improved adhesion.
U.S. Pat. No. 4,461,809 describes a surface-treating agent used as an undercoat on the surface of a polyolefin shaped article to be coated with paint. This surface-treating agent is composed of a solution of a modified polymer in organic solvent. The modified polymer is prepared by graft copolymerization of a propylene-ethylene copolymer with an alkyl ester of a monolefinic dicarboxylic acid. The alkyl moiety of the alkyl ester is described by the general formula CnH2n+1, such as methyl, ethyl, n-propyl, n-butyl, isopropyl, octyl, or 2-ethylhexyl.
U.S. Pat. No.4,632,962 describes a method for graft modifying a polyolefin with hydroxyl functional groups through an imide linkage. These modified polyolefins are made by grafting an anhydride functional group to a polyolefin chain and then reacting the anhydride group with an amine substituted organic alcohol to produce an imide. The resulting imide group on the polyolefin contains hydroxyl groups for crosslinking with various topcoats. The polyolefins are taught to be useful to produce a thermoplastic molding composition.
U.S. Pat. No. 4,966,947 describes a method for graft modifying a chlorinated polyolefin with hydroxyl functional groups through an imide linkage. These modified polyolefins are made by grafting an anhydride functional group to a chlorinated polyolefin, and then reacting the anhydride group with an amine-substituted organic alcohol to produce an imide. The resulting imide group on the chlorinated polyolefin contains hydroxyl groups for crosslinking with various topcoats.
U.S. Pat. No. 4,997,882 describes an acid- or anhydride-grafted chlorinated polyolefin that has been reacted with a monoalcohol and a polyepoxide. The composition described in this patent is prepared by grafting an unsaturated acid or anhydride onto a chlorinated polyolefin to form an acid- or anhydride-modified chlorinated polyolefin resin. This resin is then reacted with an organic monohydric alcohol to form an esterified product containing acid functionality. The resulting esterified product is then further reacted with a polyepoxide to form the ungelled modified chlorinated polyolefin resin. The resulting product is then formulated into a coating composition for a thermoplastic polyolefin substrate.
U.S. Pat. No. 5,030,681 discloses a coating resin composition obtained by graft-polymerizing an unsaturated carboxylic acid to a chlorinated polyolefin in a solvent, esterifying all unsaturated carboxylic acid present in the reaction system, and mixing the obtained composition with a urethane prepolymer.
U.S. Pat. No. 5,135,984 describes a method for modifying a chlorinated polyolefin with maleic anhydride and an acrylic-modified hydrogenated polybutadiene. This method involves the graft copolymerization of the chlorinated polyolefin with the maleic acid anhydride and acrylate modified hydrogenated polybutadiene by heating the mixture in the presence of a peroxide initiator. This results in an acrylic- and maleic anhydride-modified chlorinated polyolefin.
U.S. Pat. No. 5,143,976 describes a resin composition containing graft copolymers of acrylic monomers (A) and polydiene (B) grafted onto a chlorinated polyolefin (C). The polyolefin resin compositions composed of the acrylic oligomers contain hydroxyl or carboxyl groups and/or certain acrylic oligomers.
U.S. Pat. No. 5,523,358 describes the grafting of various unsaturated monomers to polyolefins in which an organic solvent is used to swell the polyolefin during the grafting step.
U.S. Pat. No. 5,587,418 describes a method for producing a graft copolymer for use as a primeness colored basecoat on polyolefin surfaces. The graft copolymer is obtained by copolymerizing acrylic monomers, unsaturated carboxylic acids, and acrylic monomers containing hydroxyl groups, with certain chlorinated polyolefins.
U.S. Pat. No. 5,811,489 describes a method for producing a coating resin composition based on a graft-copolymerized resin. This coating resin composition comprises a graft copolymerized resin prepared by graft copolymerizing a monomer containing an ethylenic unsaturated bond, and a monomer containing both an ethylenic unsaturated bond and a hydroxyl group, onto a mixed resin of (1) a carboxyl group-containing chlorinated polyolefin resin obtained by graft copolymerizing an unsaturated carboxylic acid or anhydride onto a polyolefin followed by chlorination and (2) a chlorinated polyolefin resin obtained by simultaneously oxidizing and chlorinating a polyolefin using at least one oxidizing agent selected from air, oxygen and ozone, an isocyanate compound or an alkyl-etherified amino resin as a curing agent.
U.S. Pat. No. 5,863,646 describes a liquid coating composition comprising a mixture of a substantially saturated polyhydroxylated polydiene polymer, having terminal hydroxyl groups, with a chlorinated polyolefin, a film forming polymer, and a carrier material. The coating can be applied to plastic substrates to improve the adhesion of subsequently applied coatings.
U.S. Pat. No. 6,001,469 describes a composition similar to that described in U.S. Pat. No. 5,863,646, and describes its use as an adhesion promoting coating that can be applied directly onto thermoplastic and thermosetting plastic substrates.
European patent application 1036817 A1 discloses a polyamide-modified polyolefin composition, which is obtained by reacting an unsaturated carboxylic acid anhydride modified polyolefin, having a specified molecular weight range, with a polyamide, having a specified molecular weight range. The resulting composition is described as having excellent adherence to polyolefin substrates without tack.
U.S. Pat. No. 6,310,134, describes solvent-based primer compositions containing 0.5 to 40 weight percent of a modified polyolefin and a solvent selected from the group consisting of ester solvents, ketone solvents, aliphatic solvents, aromatic solvents, and mixtures thereof. The polyolefins described in this report have been graft-modified with unsaturated acids, anhydrides, or esters. These modified polyolefins are reported to have good utility as primers for polyolefins substrates when topcoated with melamine based and 2-part polyurethane paints. Although these modified polyolefins provide good initial crosshatch adhesion of melamine based topcoats and good solvent resistance after application, they are deficient in water resistance, especially under high temperature and humidity conditions.
U.S. Pat. No. 6,262,182 describes a solution process for the modification of certain polyolefins with an unsaturated anhydride, unsaturated acid or unsaturated ester.